Gathered admission shook outsiders in Baltic port (6)

I believe the answer is:

gdansk

I'm a little stuck... Click here to teach me more about this clue!

'baltic port' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for gdansk that I've seen before include "Polish coastal city" , "Major Polish port" , "Polish Baltic port" , "It was once called Danzig" , "Polish city on the Baltic" .)

I've seen this clue in The Irish Times.

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